# nominatim.reverse

**beta** **Standard**

Reverse geocoding of a coordinate to the nearest address.

`GET /v1/nominatim/reverse`

> [!NOTE] **Beta.** This endpoint has not yet been verified against the live source, so fields may be missing or differ until it becomes stable. Failed calls are refunded.

## What you get

One Nominatim record in Onekey's unified shape, in `data`. If the record does not exist you get a `404 not_found` and are not charged.

## What it costs

- **Standard · 1 credit** for a fresh fetch, charged only when it succeeds.
- **Free when served from cache (0.2 credit for a cached response over 100 KB).**
- **Free** if the request is invalid (never charged) or the source fails or reports not found (refunded).

## Parameters

| Name | Type | Required | Default | What it is | Constraints |
| --- | --- | --- | --- | --- | --- |
| `lat` | string | yes | (required) | Latitude in decimal degrees (-90..90) | max 10 chars; must match `-?(?:[0-8]?\d(?:\.\d{1,6})?\|90(?:\.0{1,6})?)`; trimmed |
| `lon` | string | yes | (required) | Longitude in decimal degrees (-180..180) | max 11 chars; must match `-?(?:1[0-7]\d(?:\.\d{1,6})?\|\d{1,2}(?:\.\d{1,6})?\|180(?:\.0{1,6})?)`; trimmed |
| `zoom` | string | no | `18` | Detail level (3=country .. 18=building) | max 2 chars; must match `\d\|1[0-8]`; trimmed |

## Request

```bash
curl "https://api.onekey.dev/v1/nominatim/reverse?lat=52.52&lon=13.41" \
  -H "x-api-key: YOUR_API_KEY"
```

```python
import requests

res = requests.get(
    "https://api.onekey.dev/v1/nominatim/reverse",
    params={"lat": "52.52", "lon": "13.41"},
    headers={"x-api-key": "YOUR_API_KEY"},
)
body = res.json()

if body["success"]:
    print(body["data"])
else:
    print(body["error"]["code"], body["error"]["message"])
```

```javascript
const params = new URLSearchParams({ lat: "52.52", lon: "13.41" });
const res = await fetch(`https://api.onekey.dev/v1/nominatim/reverse?${params}`, {
  headers: { "x-api-key": "YOUR_API_KEY" },
});
const body = await res.json();

if (body.success) console.log(body.data);
else console.error(body.error.code, body.error.message);
```

## Recorded response

A real Nominatim response, recorded and returned in Onekey's shape. Fields the platform does not provide are `null`.

```json
{
  "success": true,
  "data": {
    "entity": {
      "id": "145530022",
      "name": "Klosterviertel, Spandauer Vorstadt, Mitte, Berlin, 10178, Deutschland",
      "category": "highway",
      "description": "pedestrian"
    },
    "place": {
      "lat": 52.5200175,
      "lon": 13.410084
    },
    "ext": {
      "importance": 0.05342208819714653,
      "osmType": "way",
      "osmId": "1425774289"
    }
  },
  "metadata": {
    "platform": "nominatim",
    "endpoint": "reverse",
    "cached": false,
    "stale": false,
    "age_s": 0,
    "fetched_at": "2026-01-01T12:00:00+00:00",
    "credits_charged": 1,
    "request_id": "7f3a9c2e5b1d4c8fa2e6d0b9c4f18e37"
  },
  "error": null
}
```

## Field mapping

How this endpoint's source fields become Onekey's [unified schema](https://onekey.dev/docs/schema.md). Fields the source lacks come back as `null`.

| Source path | Onekey field | Transform |
| --- | --- | --- |
| `place_id` | `entity.id` | `toString` |
| `display_name` | `entity.name` | - |
| `category` | `entity.category` | - |
| `type` | `entity.description` | - |
| `lat` | `place.lat` | `toNumber` |
| `lon` | `place.lon` | `toNumber` |
| `importance` | `ext.importance` | `toNumber` |
| `osm_type` | `ext.osmType` | - |
| `osm_id` | `ext.osmId` | `toString` |

## Caching and freshness

- Fresh for about 30 minutes. Repeat calls in that window are served from cache and are free.
- Between 30 minutes and 6 hours the cached copy is still served instantly and marked `stale: true` while Onekey refreshes it in the background.
- If the source is down when a refresh is needed, the last copy can be served for up to 1 day more (marked stale).
- A "not found" is remembered for 5 minutes and is free.
- The cache is shared across all customers, which is what keeps repeat calls cheap.

## What can go wrong

| Status | Code | What to do |
| --- | --- | --- |
| 401 | `unauthorized` | Check the `x-api-key` header. |
| 402 | `insufficient_credits` | [Add credits](https://onekey.dev/pricing); your balance must cover the price. |
| 404 | `not_found` | That record does not exist. Free; do not retry. |
| 422 | `invalid_params` | Fix the parameters using the table above. Free. |
| 429 | `rate_limited` | Wait `Retry-After` seconds, then retry. |
| 502 | `upstream_error` | The source failed. Refunded; retry with backoff. |

See [Errors](https://onekey.dev/docs/errors.md) for the full list and retry guidance.

Status: beta (not yet verified against the live source).